1. Field of the Invention
This invention relates to a learning air-fuel ratio control system for use with an electronic control fuel injection engine, which computes fuel injection amount and the like by means of a digital processor.
2. Description of the Prior Art
In a conventional learning air-fuel ratio control system for an electronic control engine, the final fuel injection amount TAU is defined, for example, as follows; EQU TAU=A.times.TP+K1 (1)
or EQU TAU=K2.times.TP+B (2) PA1 TP: basic fuel injection amount as function F(L) of engine load L PA1 K1, K2: constant or correction amount due to intake air temperature.
where A, B: learning terms
With either type of control, only a single learning term is employed. During the learning control, either A in formula (1) or B in formula (2) is corrected in relation to feedback signals from an air-fuel ratio sensor. However, in the formula (1), sufficient learning effect cannot be obtained during idling period, so that the stability of control or purification of exhaust gas is deteriorated. In the formula (2), sufficient learning effect cannot be obtained during running with high load, so that the purification of exhaust gas and the engine running performance (drive ability) are deteriorated.